The invention is directed to a method for manufacturing an adhesion layer for a heat insulation layer that is applied onto a component part.
Thermally or mechanically stressed component parts are provided with protective layers, for example anti-wear layers or heat insulation layers. An adhesion layer is generally provided between such an outer layer and the component part. Such adhesion layers must comprise a certain roughness and surface topography for clamping to the outer layer.
In gas turbine engineering with, for example, highly thermally stressed, metallic component parts such as turbine blades, the adhesion layers blades are provided between the component part and a heat insulation layer. Such heat insulation layers can be composed of a basis of zirconium oxide with additives of calcium oxide or magnesium oxide. In addition to the roughness for clamping to the outer protective layer or, respectively, the heat insulation layer, the adhesion layers must be oxide free and resistant to hot-gas corrosion. Since different thermal expansions generally occur in the heat insulation layer and the material of the metallic component part, these must also be at least partially compensated by the adhesion layer.
Diffusion layers that contain Al, Cr or Si are known as adhesion layers, these being manufactured by what is referred to as a powder packing method or out-of-pack method. The disadvantage of the diffusion layers manufactured with these methods are their brittleness and the limited layer thicknesses of up to approximately 100 xcexcm.
Another known layer, what is referred to as a seating layer, on a MCrAlY basis is sprayed onto the component part with plasma spraying or is vapor-deposited onto the component part with evaporation of the layer constituents in an electron beam. Layer thicknesses up to approximately 300 xcexcm are thereby achieved. Such methods are extremely complicated and expensive in terms of fabrication technology. Further disadvantages are that the layers cannot be uniformly applied onto geometrically complicated component parts, scatters in the layer composition occur, and the layer elements oxidize when being sprayed on or, respectively, when being vapor-deposited.
JP 55-82761 A discloses that component parts of, for example, a gas turbine, which parts are exposed to hot gases, can be protected in that Ni powder, which is provided with a bonding agent, is first applied onto the component part and is heat-treated, Cr is then introduced by chemical vapor-phase deposition or Al is introduced by a packing method, and, finally, Pt, Pd or Rh are deposited and heat-treated.
The object of the present invention is comprised in creating a method for manufacturing a layer of the species initially described that can be manufactured optimally simply in fabrication-oriented terms and cost-beneficially.
The attainment of this object is inventively characterized by the steps:
a) producing a slip by mixing powder containing at least one of the elements Cr, Ni or Ce with a binding agent;
b) applying the slip onto the component part;
c) drying the slip at temperatures from room temperature through 300xc2x0 C.; and
d) alitizing or aluminizing the slip layer to form an adhesive layer, whereby the method is controlled so that the adhesion layer comprises a structure having a grain size less than 75 xcexcm and a cavity proportion from 0 through 40%.
The advantage of the method is that the powder mixed with a binding agent can be applied onto the component part in a simple way upon formation of a layer without requiring methods such as plasma spraying or electron beam evaporation that are expensive in terms of the outlay for systems. The layers manufactured with this method have a comparatively fine-grained structure with a grain size that is smaller than 75 xcexcm. The layer comprises a cavity proportion from 0 through 40%. As a result, the layer has an improved thermal fatigue resistance as well as an advantageous expansion behavior that is error-tolerant with respect to cracks. Moreover, additives of elements such as, for example, Y are uniformly distributed and not oxidized.
In a preferred development of the method, the slip is produced with a powder of MCrAlY or, respectively, a MCrAlY alloy, whereby M stands for at least one of the elements Ni, Co, Pt or Pd and instead of Y, Hf or Ce can also be employed.
The powder is preferably present with a grain size distribution from 5 through 120 xcexcm.
The application of the slip onto the component part preferably ensues by spraying, brushing or immersion, as a result whereof the method can be simply and cost-beneficially implemented in terms of fabrication technology. As a result of this type of application, locally limited layers can also be applied to geometrically complicated component parts in a simple way. Moreover, no expensive and complicated spraying and evaporation systems are required. Differing from thermal spraying or electron beam vapor-deposition, moreover, the problem of oxidation of the powder particles does not occur.
The drying of the slip, which is present in a suspension together with the organic or inorganic binding agent, is preferably implemented over 0.5 through 4 hours, whereby a duration of 1 through 2 hours has proven advantageous.
It is also preferred that the slip layer is heat-treated at temperatures from 750 through 1200xc2x0 C. in argon or a vacuum before the alitizing, whereby the heat treatment can be implemented over 1 through 6 hours in order to bond the slip layer to the component part by diffusion.
In a preferred development of the method, the final step of alitizing or aluminizing the slip layer is implemented at a temperature between 800 and 1200xc2x0 C. and a duration of 1 through 12 hours. The aluminizing serves the purpose of diffusion joining and compacting the layer and is implemented in a standard method such as, for example, in the powder pack method upon introduction of Al. The Al diffuses into the layer and into the basic material of the component part.
The layer is also preferably an adhesion layer onto which a heat insulation layer is applied as an outer layer or, respectively, protective layer, this potentially ensuing in a standard way by plasma spraying or electron beam vapor-deposition.
The invention is explained in greater detail with reference to the drawings.